A vehicle, such as, for example, an on or off highway truck, may include a compression release braking system that assists a conventional braking system in reducing the speed of the vehicle. The compression release braking system allows an internal combustion engine to convert the kinetic energy of the moving vehicle into compressed air in the combustion chambers of the engine. The compression release braking system releases the compressed air from the combustion chambers to the environment to thereby dissipate the kinetic energy of the moving vehicle and slow the vehicle.
A compression release braking system typically cooperates with a valve actuation system connected with the engine. The compression release braking system opens the exhaust valves of the engine when a piston associated with each combustion chamber is at or near a top-dead-center position of a compression stroke. Opening the exhaust valve allows the air compressed by the piston in the combustion chamber during the compression stroke to escape from the combustion chamber through an exhaust passageway. In this manner, the pistons of the engine are used as air compressors to absorb power instead of generating power in response to the combustion of fuel.
The compression release braking system may also operate in conjunction with a fuel delivery system. When an operator instructs the vehicle to slow down, such as, for example, by depressing a brake pedal, the fuel delivery system may stop delivering fuel to the combustion chambers. This will conserve fuel by preventing fuel from being exhausted from the combustion chambers with the release of compressed air. In addition, stopping fuel delivery during engine braking will prevent an inadvertent ignition of fuel during the combustion stroke before the exhaust valves are opened to release the compressed air.
A compression release braking system may operate with a conventional cam driven engine valve actuation system. The compression release braking system may include a hydraulically powered engine valve actuator that engages and opens an exhaust valve independently of the cam driven system. The compression release braking system may also include a directional control valve that controls a flow of pressurized fluid to the piston to coordinate the opening of the exhaust valves with the movement of the piston.
The amount of movement of each exhaust valve should be controlled to prevent damage to the exhaust valve. If the engine valve actuator moves the exhaust valve too far into the combustion chamber, the exhaust valve may come into contact with the piston, which will be approaching the exhaust valve as it nears a top-dead-center position during the compression stroke. Contact between the exhaust valve and the piston can result in damage to the exhaust valve, which may detract from engine performance when conventional engine operation is resumed.
To prevent damage to the exhaust valves, an engine valve actuator may be configured to limit the amount of motion of the hydraulically powered piston to thereby limit the amount of motion of the exhaust valve. For example, as shown in U.S. Pat. No. 5,161,501 to Hu, the travel distance of a piston in an engine valve actuator may be limited by opening a fluid escape passage in the actuator housing after the piston has moved through a certain distance. The fluid escape passageway allows the release of the pressurized fluid that is driving the piston to thereby decrease the force acting on the piston. Therefore, the piston will stop moving when the fluid escape passageway is opened.
However, the engine valve actuator described in U.S. Pat. No. 5,161,501 requires precise positioning relative to the engine valve. The travel distance of the piston is limited by the fluid passageway in the brake housing. Accordingly, the actuator housing must be positioned in sufficient proximity to the engine valve to ensure that the piston will engage and open the exhaust valve before the fluid escape passageway is opened. Thus, the compression release braking system described in U.S. Pat. No. 5,161,501 to Hu is relatively inflexible and does not provide for individual valve actuator adjustment.
The engine valve actuator of the present disclosure solves one or more of the problems set forth above.